THE DETERMINATION OF SEX 275 



that Whitney and A. F. Shull, each working separately 

 on rotifers, have been able, through modification of ex- 

 ternal conditions, to alter the normal cycle of repro- 

 duction, by causing the continuance of the partheno- 

 genetic process beyond the normal limit. 



It seems evident that, through the modification of 

 external conditions, they have succeeded in influencing 

 the type of egg produced. If this case is really paral- 

 lel to that of Aphis and Phylloxera, then the type of 

 egg artificially produced ought thereafter to control 

 its own maturation. 



In daphnids, where parthenogenesis alternates with 

 the sexual cycle, at least three kinds of eggs are pro- 

 duced; (1) thick-shelled, fat-laden, ephippial eggs 

 which must be fertilized in order to develop; (2) thin- 

 shelled, glycogen-laden, parthenogenetic eggs, which 

 develop into females without fertilization; and (3) 

 thin-shelled, smaller, parthenogenetic eggs which de- 

 velop into males. The type of egg produced, as 

 shown by Smith, may be influenced by temperature and 

 also by food. It is not improbable that we may yet 

 discover in the maturation of these ova differences in 

 chromosomal behavior correlated with each type of 

 ovum and the sex of the resulting offspring. 



C. THE HONEY BEE 



Closely allied to the problem of the sex cycle, as 

 described in experiments with the homopterons, is the 

 question of sex-determination as observed in the 

 hym^noptera. 



